1. Field of the Invention
This invention relates generally to motor vehicle shock absorbers and more particularly to an improved valve construction for a shock absorber.
2. Disclosure Information
Telescopic shock absorbers commonly have a working cylinder with a piston assembly slideably received therein. Commonly, the cylinder is fixed to an unsprung member such as a suspension arm whereas the piston assembly is fixed to a piston rod that in turn is fixed to a sprung member such as a chassis frame. The cylinder is filled with fluid. The piston has passageways therethrough which restrict fluid flow between a chamber within the pressure tube defined below the piston and a chamber defined above the piston. The restricted fluid flow damps the motion of the piston relative to the cylinder. The passageways in the piston are often opened and closed by spring biased disc valves to give the shock absorber a high or low damping characteristic.
Usually, a double acting shock absorber has a valve element closing off the jounce ports during a rebound stroke and a second valve element closing off the rebound ports during a jounce stroke. During each jounce stroke, fluid passes through the jounce port and forces open the valve covering the jounce ports against a spring bias. In a similar manner during each rebound stroke, fluid passes through the rebound ports and forces open the second valve element against its spring bias.
Shock absorbers are desired to provide a soft ride on smooth road surfaces and yet have a capacity to dampen severe shocks when the vehicle encounters potholes and large bumps. Consequently, telescopic shock absorbers incorporated into motor vehicles are often constructed with a compromised damping characteristic.
Particular problems occur in MacPherson style suspensions which incorporate a shock absorber in a telescopic strut. If the piston valve does not provide sufficient damping, the piston can reach its stroke limit and abut either the bottom or the top end of the cylinder or a stop bumper which cause severe jarring to the vehicle. On the other hand, if the piston provides for too much damping, the piston can lock up within the cylinder and cause the shock absorber to be inoperable under certain conditions. As a result, a passenger may feel annoying small vibrations during operation of the vehicle on relatively smooth road surfaces.
Certain telescopic shock absorbers allow for low damping characteristics when the piston is centrally located in the pressure tube and produce higher damping forces when the piston is near either end of the pressure tube. However, the damping characteristics are dependent on the position of the piston. When a large pothole or bump is encountered, it is desirable for the piston to have a large damping force before it reaches the extremity of its stroke.
What is needed is a piston valve that normally provides low amount of damping but provides high damping control when needed independent from the position of the piston in the pressure tube.